The present invention relates to a ceramic plasma reactor for generating a plasma by introducing gas between two unit electrodes and a plasma reaction apparatus.
There has been known the fact that silent discharge is caused by applying alternating high voltage or periodic pulse voltage with a dielectric body being disposed between two electrodes to form active species, radicals, and ions in a plasma field formed by the silent discharge, thereby accelerating reaction and decomposition of gas, and that this can be used for removal of harmful components contained in engine exhaust gas or various kinds of incinerator gas.
Since a coaxial cylindrical reactor shown in JP-A-2005-222779 has different electric fields between the central portion and the outer peripheral portion though it has a simple structure, it causes a difference in plasma treatment efficiency, and a large capacity is required in the case of quickly treating a large amount of gas such as automobile exhaust gas purification or fuel reforming.
Since a parallel flat plate type reactor shown in WO2005/1250 pamphlet can give a uniform electric field in a large space, a uniform plasma field can easily be formed by combining with a power source having a small pulse width, and gas can be reformed efficiently by a small reactor by superimposing each other electrodes to have multistages. However, in a gas circulation direction, an efficient gas reaction proceeds in the front portion since much untreated gas is present, but an untreated gas decreases as the gas flows and there arises a problem of inefficient reaction caused in the back portion with respect to the input energy.
In a semiconductor process, a parallel flat plate type reactor is used. JP-A-2004-296553 discloses a structure where through-holes are aligned in the upper electrode, and reaction gas is allowed to flow perpendicularly to the flat plate electrode, thereby supplying untreated gas in all the portions. However, it was difficult to downsizing the apparatus for vehicle installation though the disclosed technique can be applied to a semiconductor-manufacturing process apparatus capable of surrounding the reactor by a large chamber.
WO2004/114728 pamphlet discloses an electrode where a conductor having a through-hole is embedded therein. Since discharge is not caused in the through-hole portion of the conductive film, the gas passing through this portion does not have a plasma reaction. Therefore, the reaction efficiency on the back side can be made higher than in the case where the entire face discharges. However, high efficiency cannot be obtained sufficiently.
Therefore, there has been required a plasma reactor having a parallel flat plate type electrode structure, capable of effectively utilizing a plasma even at the back of the discharge portion with respect to the gas flow, and having high energy efficiency. The present invention aims to provide a small-sized ceramic plasma reactor capable of efficiently treating gas by generating plasma with introducing the gas between the unit electrodes and to provide a plasma reaction apparatus.